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Abstract: The polyharmonic Navier problem is considered, the uniqueness (non-uniqueness) of its solution is studied in unbounded domains under the assumption that the generalized solution of this problem has a finite Dirichlet integral with weight \( x ^a\) . Depending on the values of the parameter \(a\) , uniqueness theorems are proved and exact formulas are found for calculating the dimension of the space of solutions of the Navier problem for a polyharmonic equation in the exterior of a compact set and in a half-space. DOI 10.1134/S1061920823040209 PubDate: 2023-12-01

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Abstract: It is proved that if \(G\) is a connected solvable group and \(\pi\) is a (not necessarily continuous) representation of \(G\) in a finite-dimensional vector space \(E\) , then there is a basis in \(E\) in which the matrices of the representation operators of \(\pi\) have upper triangular form. The assertion is extended to connected solvable locally compact groups \(G\) having a connected normal subgroup for which the quotient group is a Lie group. DOI 10.1134/S1061920823040180 PubDate: 2023-12-01

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Abstract: We consider the Hamiltonian system consisting of the Klein–Gordon field coupled to an infinite harmonic crystal. The dynamics of the coupled system is translation-invariant with respect to the space translations in \(\mathbb{Z}^d\) , \(d\ge1\) . We study the Cauchy problem and assume that the initial date is a random function. We introduce the family of initial probability measures \(\{\mu_0^\varepsilon,\varepsilon >0\}\) slowly varying on the linear scale \(1/\varepsilon\) . For times of order \(\varepsilon^{-\kappa}\) , \(0<\kappa\le1\) , we study the distribution of a random solution and prove the convergence of its covariance to a limit as \(\varepsilon\to0\) . If \(\kappa<1\) , then the limit covariance is time stationary. In the case when \(\kappa=1\) , the covariance changes in time and is governed by a semiclassical transport equation. We give an application to the case of the Gibbs initial measures. DOI 10.1134/S1061920823040076 PubDate: 2023-12-01

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Abstract: We study a system of two integro-differential equations that arises as the result of linearization of Boltzmann–Maxwell’s kinetic equations, where the collision integral is chosen in the Bhatnagar–Gross–Krook approximation, and the unperturbed state of the plasma is characterized by the Fermi–Dirac distribution. The unknown functions are the linear parts of the perturbations of the distribution function of the charged particles and the electric field strength in plasma. In the paper, an analytical representation for the general solution of this system is found. When deriving this representation, some new results were applied to Fourier transforms of distributions (generalized functions). DOI 10.1134/S1061920823040039 PubDate: 2023-12-01

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Abstract: The aim of this paper is to study probabilistic versions of the degenerate Stirling numbers of the second kind and the degenerate Bell polynomials, namely the probabilisitc degenerate Stirling numbers of the second kind associated with \(Y\) and the probabilistic degenerate Bell polynomials associated with \(Y\) , which are also degenerate versions of the probabilisitc Stirling numbers of the second and the probabilistic Bell polynomials considered earlier. Here \(Y\) is a random variable whose moment generating function exists in some neighborhood of the origin. We derive some properties, explicit expressions, certain identities and recurrence relations for those numbers and polynomials. In addition, we treat the special cases that \(Y\) is the Poisson random variable with parameter \(\alpha (>0)\) and the Bernoulli random variable with probability of success \(p\) . DOI 10.1134/S106192082304009X PubDate: 2023-12-01

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Abstract: In the paper, using Krein’s resolvent formula, we find an asymptotics of the resolvent of the trace of the Laplace operator on a metric graph. DOI 10.1134/S1061920823040192 PubDate: 2023-12-01

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Abstract: The paper is devoted to the study of a billiard bounded by an ellipse and equipped with a fourth degree potential as an integrable Hamiltonian system with two degrees of freedom. In previous works, the author described the structure of the Liouville foliation of such a system on nonsingular levels of the Hamiltonian in terms of Fomenko–Zieschang invariants: marked molecules and 3-atoms. Moreover, the dependence of the structure of the bifurcation diagram on the parameters of the potential has been established. The present work continues this study. Thus, the structure of the Liouville foliation in a neighborhood of critical layers containing a nondegenerate singular point of rank 0 or a degenerate orbit has been described. A classification of the obtained semilocal singularities was given. Finally, connections of our system with well-known cases of rigid body dynamics containing equivalent singularities is established. DOI 10.1134/S1061920823040155 PubDate: 2023-12-01

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Abstract: The paper considers the Cauchy problem for a multidimensional quasilinear hyperbolic system of differential equations with the data rapidly oscillating in time. This data do not explicitly depend on spatial variables. The method by N. M. Krylov–N. N. Bogolyubov is developed and justified for these systems. Also an algorithm is developed and justified, based on this method and the method of two-scale expansions, for constructing the complete asymptotics of solutions. DOI 10.1134/S1061920823040118 PubDate: 2023-12-01

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Abstract: The Pauli–Jordan–Dirac anticommutator mean-square formula is presented. DOI 10.1134/S1061920823040088 PubDate: 2023-12-01

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Abstract: We consider the \(L_{p}\) -theory of interaction problems associated with Dirac operators with singular potentials of the form \(D=\mathfrak{D}_{m,\Phi }+\Gamma\delta_{\Sigma}\) where $$\mathfrak{D}_{m,\Phi}=\sum_{j=1}^{n}\alpha_{j}(-i\partial_{x_{j}} )+m\alpha_{n+1}+\Phi\mathbb{I}_{N}$$ is a Dirac operator on \(\mathbb{R}^{n}\) , \(\alpha_{1},\alpha_{2},\dots,\alpha _{n},\alpha_{n+1}\) are Dirac matrices, \(m\) is a variable mass, \(\Phi \mathbb{I}_{N}\) electrostatic potential, \(\Gamma\delta_{\Sigma}\) is a singular potential with support on smooth hypersurfaces \(\Sigma \subset\mathbb{R}^{n}.\) We associate with the formal Dirac operator \(D\) the interaction (transmission) problem on \(\mathbb{R}^{n}\diagdown\Sigma\) with the interaction conditions on \(\Sigma\) . Applying the method of potential operators we reduce the interaction problem to a pseudodifferential equation on \(\Sigma.\) The main aim of the paper is the study of Fredholm property of these pseudodifferential operators on unbounded hypersurfaces \(\Sigma\) and applications to the study of Fredholmness of interaction problems on unbounded smooth hypersurfaces in Sobolev and Besov spaces. DOI 10.1134/S1061920823040167 PubDate: 2023-12-01

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Abstract: In this paper, equations describing a double-dimensional flow along a curved smooth plate with small periodic irregularities are derived. The parameters of the irregularities are chosen so that the flow has a double-deck structure. The equations describing the terms of the asymptotic solution are written in the original coordinate system, which required changes in the form of the usual ansatz. DOI 10.1134/S1061920823040040 PubDate: 2023-12-01

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Abstract: An asymptotically exact estimate for the norm of the difference between a function and the partial sum of its Fourier series is obtained in terms of the modulus of continuity of the function. The values of the modulus of continuity of the argument that are less than the optimal one are considered. DOI 10.1134/S1061920823040179 PubDate: 2023-12-01

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Abstract: We study the asymptotic solution of the Cauchy problem with rapidly changing initial data for the one-dimensional nonstationary Schrödinger equation with a smooth potential perturbed by a small rapidly oscillating addition. Solutions to such a Cauchy problem are described by moving, rapidly oscillating wave packets. According to long-standing results of V.S. Buslaev and S.Yu. Dobrokhotov, the construction of a solution to this problem can be constructed applying the sequential use of the adiabatic and semiclassical approximations. In the general situation, the construction the asymptotic formula reduces to solving a large number of auxiliary spectral problems for families of Bloch functions of ordinary differential operators of Sturm–Liouville type, and the answer is presented in an ineffective form. On the other hand, the assumption that the rapidly oscillating perturbation of the potential is small gives the opportunity, firstly, to write asymptotic formulas for solutions of the indicated auxiliary spectral problems and, secondly, to save, in the construction of the answer to the original problem, only finitely many these problems and their solutions. Bounds are obtained for problem parameters answering when such considerations can be implemented and, if the corresponding conditions on the parameters are satisfied, asymptotic solutions are constructed. DOI 10.1134/S1061920823040052 PubDate: 2023-12-01

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Abstract: In the paper, three-dimensional Nijenhuis operators are studied that have differential singularities, i.e., such points at which the coefficients of the characteristic polynomials are dependent. The case is studied in which the differentials of all invariants of the Nijenhuis operator are proportional, as well as the case when two invariants are functionally independent and the third defines a fold-type singularity. In particular, new examples of three-dimensional Nijenhuis operators with singularities of the specified type are constructed. DOI 10.1134/S1061920823040015 PubDate: 2023-12-01

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Abstract: We consider the eigenproblem for the Laplacian inside a three-dimensional domain of revolution diffeomorphic to a solid torus, and construct asymptotic eigenvalues and eigenfunctions (quasimodes) of the whispering gallery-type. The whispering gallery-type asymptotics are localized near the boundary of the domain, and an explicit analytic representation in terms of Airy functions is constructed for such asymptotics. There are several different scales in the problem, which makes it possible to apply the procedure of adiabatic approximation in the form of operator separation of variables to reduce the initial problem to one-dimensional problems up to a small correction. We also discuss the relationship between the constructed whispering gallery-type asymptotics and classical billiards in the corresponding domain, in particular, such asymptotics correspond to almost integrable billiards with proper degeneracy. We illustrate the results in the case when a domain of revolution is obtained by the rotation of a triangle with rounded wedges. DOI 10.1134/S1061920823040131 PubDate: 2023-12-01

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Abstract: In \(L_2(\mathbb{R}^d)\) , we consider an elliptic differential operator \(\mathcal{A}_\varepsilon \! = \! - \operatorname{div} g(\mathbf{x}/\varepsilon) \nabla + \varepsilon^{-2} V(\mathbf{x}/\varepsilon)\) , \( \varepsilon > 0\) , with periodic coefficients. For the nonstationary Schrödinger equation with the Hamiltonian \(\mathcal{A}_\varepsilon\) , analogs of homogenization problems related to an arbitrary point of the dispersion relation of the operator \(\mathcal{A}_1\) are studied (the so called high-energy homogenization). For the solutions of the Cauchy problems for these equations with special initial data, approximations in \(L_2(\mathbb{R}^d)\) -norm for small \(\varepsilon\) are obtained. DOI 10.1134/S1061920823040064 PubDate: 2023-12-01

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Abstract: The article studies (locally) holomorphically homogeneous real hypersurfaces of complex spaces. Currently, the problem of classifying such hypersurfaces is completely solved only in the spaces \(\mathbb{C}^{2}\) and \(\mathbb{C}^{3}\) . As the dimension of the ambient space grows, so does the relative part of Levi-degenerate manifolds in the family of all homogeneous hypersurfaces. In particular, this family includes holomorphically degenerate hypersurfaces, which are (locally) direct products of homogeneous hypersurfaces from spaces of smaller dimensions and spaces \(\mathbb{C}^{k}\) . The article proves a sufficient Levi-degeneracy condition of all orbits in spaces \(\mathbb{C}^{n+1}\) \((n \ge 3)\) for \((2n+1)\) -dimensional Lie algebras of holomorphic vector fields having full rank at the points in \(\mathbb{C}^{n+1}\) . The proven condition is the existence of an abelian subalgebra of codimension 2 in the Lie algebra under discussion. It is shown that in the case \(n = 3\) , this condition holds for a large family of 7-dimensional Lie algebras. Holomorphically homogeneous hypersurfaces, i.e. the orbits of these algebras in \(\mathbb{C}^{4}\) can only be Levi-degenerate manifolds. We provide an example of a family of 7-dimensional Lie algebras that have 5-dimensional abelian ideals and Levi-degenerate (but not holomorphically degenerate) orbits. DOI 10.1134/S1061920823040027 PubDate: 2023-12-01

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Abstract: The Cauchy problem for a one-dimensional (nonlinear) shallow water equations over a variable bottom \(D(x)\) is considered in an extended basin bounded from two sides by shores (where the bottom degenerates, \(D(a)=0\) ), or by a shore and a wall. The short-wave asymptotics of the linearized system in the form of a propagating localized wave is constructed. After applying to the constructed functions a simple parametric or explicit change of variables proposed in recent papers (Dobrokhotov, Minenkov, Nazaikinsky, 2022 and Dobrokhotov, Kalinichenko, Minenkov, Nazaikinsky, 2023), we obtain the asymptotics of the original nonlinear problem. On the constructed families of functions, the ratio of the amplitude and the wavelength is studied for which hte wave does not collapse when running up to the shore. DOI 10.1134/S1061920823040143 PubDate: 2023-12-01

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Abstract: The paper is devoted to describing the dynamics and uprush of time-periodic long waves in basins with gentle shores. We consider waves that are defined by solutions localized between caustics in the domain bounded by the shores of the basin. We also consider solutions localized in the vicinity of a periodic trajectory which, during the period, has exactly two intersections with the boundary of such a domain. DOI 10.1134/S1061920823040106 PubDate: 2023-12-01

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Abstract: In \(L_2(\mathbb{R}^d;\mathbb{C}^n)\) , we consider a matrix elliptic second order differential operator \(B_\varepsilon >0\) . Coefficients of the operator \(B_\varepsilon\) are periodic with respect to some lattice in \(\mathbb{R}^d\) and depend on \(\mathbf{x}/\varepsilon\) . We study the quantitative homogenization for the solutions of the hyperbolic system \(\partial _t^2\mathbf{u}_\varepsilon =-B_\varepsilon\mathbf{u}_\varepsilon\) . In operator terms, we are interested in approximations of the operators \(\cos (tB_\varepsilon ^{1/2})\) and \(B_\varepsilon ^{-1/2}\sin (tB_\varepsilon ^{1/2})\) in suitable operator norms. Approximations for the resolvent \(B_\varepsilon ^{-1}\) have been already obtained by T.A. Suslina. So, we rewrite hyperbolic equation as a system for the vector with components \(\mathbf{u}_\varepsilon \) and \(\partial _t\mathbf{u}_\varepsilon\) , and consider the corresponding unitary group. For this group, we adapt the proof of the Trotter-Kato theorem by introduction of some correction term and derive hyperbolic results from elliptic ones. DOI 10.1134/S106192082304012X PubDate: 2023-12-01